The invention relates to collection and analysis of data for the purposes of predictive maintenance.
There are many well known methods for collecting data for performing predictive maintenance. Typically, in these methods a vibration sensor such as a piezoelectric accelerometer is mechanically coupled to the machine to be monitored. The vibration sensor collects vibrations from the machine and converts these vibration to an electrical signal. The electrical signal is processed by suitable signal processing and converted from analog to digital form. The resulting digital signal is stored for later analysis.
Often it is necessary to evaluate the rotational speed of the machine being monitored as part of the collection of vibration data. This is often done through the use of a tachometer mounted to the machine or used with the machine. A difficulty arises when no such tachometer is available. To deal with this situation, a portable tachometer must be used. U.S. Pat. No. 5,059,901, owned by the assignee of the present application, and incorporated by reference herein in its entirety, describes one such portable tachometer. The tachometer described in U.S. Pat. No. 5,059,901 utilizes laser light to measure rotational speed of a machine. Specifically, a laser provides a beam of light, visible even under extremely bright ambient light conditions, to be used to measure the rotational speed of a rotating device from greater distances than previously possible. A diverging beam of laser light is collimated and transmitted to a rotating body the RPM of which is to be measured. The rotating body includes a reflective strip or strips, so that during rotation the reflection of the beam is modulated. The modulated reflected light is received by the tachometer where it is focused onto a photodetector, which converts it into an electrical signal representative of the speed of the rotating body.
Analysis of a vibration signal from a machine typically involves one or both of (1) comparing that signal to previously collected signals to identify an variations that would be indicative of machine wear and possible impending failure, and (2) forming a frequency spectrum of the vibration signal and evaluating this spectrum for patterns indicative of potential failures. Typically these operations are performed through the use of a data collector. A data collector includes analog signal processing electronics for receiving a vibration signal and conditioning that signal, and an analog to digital converter for digitally sampling the analog signal so that it may be stored and analyzed. Often a first vibration signal is used as a trigger or reference signal in connection with the collection of a second vibration signal, in which case two accelerometers are used. Signal analysis may be performed using the data collector itself or by uploading collected and digitized signals from the data collector to a host computer where signal analysis is performed.
It will be appreciated that a data collector is typically portable, to facilitate its use in an industrial environment. A technician will carry the data collector to the machines being monitored and then collect vibration and speed data at each machine. Unfortunately, however, when a laser tachometer is being used, the collected devices may be cumbersome to handle, as the laser tachometer must be held in-hand and sighted to the location of the rotating body being used as the tachometer reference. At the same time, one or two accelerometers must be held or mounted to the machine to collect vibrations. And, of course, the data collector itself must be held or placed on a surface where its display can be read and keys can be reached, during this process. Thus, the use of all of these features in a portable data collector is an inconvenient process and requires complex manipulation of the collector and its various attachments.
Accordingly, there is a need for a data collector and data collection method utilizing a laser tachometer that is more convenient and less complex and thus can be more readily used in a wide range of applications.
In accordance with principles of the present invention, this need is met by a data collector having an integrated tachometer device.
Specifically, a data collector in accordance with principles of the present invention comprises a housing, a vibration signal input on the housing for receiving a vibration signal to be digitized, an optical system in the housing receiving light from outside said housing to be converted to a digital signal, and a digital signal processing circuit receiving, storing or processing the digitized vibration signal and/or the digital signal converted from said received light, for the purpose of predictive maintenance.
In the specific embodiment disclosed herein, a light source emits light from the housing through an aperture, for reflection and return to the optical system. The light is generated by a laser diode, collimated by a collimating lens. A filter is positioned between the housing aperture and the PIN diode, to filter light other than at a wavelength of the light source. The reflected light is detected by a PIN diode. Reflected light is directed to the PIN diode by a beam splitter in the optical system. A threshold comparator compares current flow in the PIN diode to a threshold, and produces a digital signal to the digital signal processing circuit when said threshold is exceeded, so that the processing circuit may compute a rate of rotation of a moving element in response to timing of the digital signal from said threshold comparator, thus forming a laser tachometer. Rotational speed information generated from the integrated tachometer, may thus be used by the data collector as part of analyzing or storing the digitized vibration signal.
The housing of the data collector in the disclosed embodiment also holds a display and input keys, and is sized to fit in a single hand of an operator. As a consequence, an operator may use the same hand for holding and controlling the data collector, and for holding the laser light source for the laser tachometer. This frees a hand for holding an accelerometer or for other purposes. Use of a data collector with an integrated laser tachometer, in accordance with principles of the present invention, is thus substantially more convenient than using a data collector with a separate, nonintegrated laser tachometer attachment. The invention thus provides substantial improvement in the process of data collection over the prior art.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.